Nullable. Consider an Integer in VB.NET. It cannot be null—it can only have a numeric value. But we can wrap the Integer inside a nullable Structure, which can logically be Nothing.
With properties and functions, we can test a Nullable. We specify a nullable type by adding a question mark after the type name. For the value, we can access Value.
An example. Here we see a nullable Integer named "element." We use the Integer in various ways. We use the Nothing value to indicate "null" in the VB.NET language.
Note The HasValue property returns true or false. It indicates whether an underlying value is contained in the nullable.
Note 2 The GetValueOrDefault function safely returns the underlying value. If the nullable has no value, it returns the value type's default.
Finally The Value property will throw an exception if the nullable has no value. Prefer GetValueOrDefault to avoid exceptions.
Module Module1
Sub Main()
' A nullable can be Nothing.
Dim element As Integer? = Nothing
Console.WriteLine("HASVALUE: {0}", element.HasValue)
Console.WriteLine("GETVALUEORDEFAULT: {0}", element.GetValueOrDefault())
' Use an Integer value for the nullable Integer.
element = 100
Console.WriteLine("VALUE: {0}", element.Value)
Console.WriteLine("GETVALUEORDEFAULT: {0}", element.GetValueOrDefault())
End Sub
End ModuleHASVALUE: False
GETVALUEORDEFAULT: 0
VALUE: 100
GETVALUEORDEFAULT: 100
Notes, null. In VB.NET the keyword "Nothing" is used to indicate null. This makes types like nullable somewhat confusing, because they are based on C# terms.
A summary. What is a null Integer or other null value type? A null thing can be used to indicate an uninitialized value—we can have uninitialized, or an actual number set.
In this way, nullable types can help eliminate ambiguous parts of programs. We do not need to use -1 as a special value meaning "not set." We can use null.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Jun 19, 2023 (edit).